Power management on a data processing system often involves techniques for reducing the consumption of power by components in the data processing system. The data processing system may be a laptop or otherwise portable computer, such as a handheld general purpose computer or a cellular telephone. The management of power consumption in a portable device which is powered by a battery is particularly important because better power management usually results in the ability to use the portable device for a longer period of time when it is powered by one or more batteries.
Conventional systems typically utilize timers to indicate when a subsystem should be turned off after a period of inactivity. For example, the motors in a hard drive storage system are typically turned off after a predetermined period of inactivity of the hard drive system. Similarly, the backlight or other light source of a display system may be turned off in response to user inactivity which exceeds a predetermined period of time. In both cases, the power management technique is based on the use of a timer which determines when the period of inactivity exceeds a selected duration.
In other power managing techniques, the data processing system may be switched between different operating points. An operating point may represent a particular operating voltage and frequency pair. For example, one operating point consumes less power by having the data processing system operate at a lower voltage and also at a lower operating frequency relative to another operating point. In the case of another operating point, the data processing system operates at a higher voltage and a higher operating frequency.
Certain systems provide the capability to switch power completely off (e.g. set the operating voltage at V=0) if no use is being made of a particular subsystem. For example, certain systems on a chip (SOCs) provide a power saving feature which allows for particular subsystems to be turned off completely if they are not being used.
Existing power management techniques typically manage the power based on the theoretical assumptions. The existing power management techniques typically do not take into account the actual states of the system components. Such techniques lack accuracy, reliability, and are unable to efficiently manage the power of the digital processing system.
Some existing power management techniques may manage power of a component using the local information. These techniques typically have control of power only over a single component and do not have control of power over the other components in the system. In such techniques, for example, the power of a central processing unit (“CPU”) may be controlled based on the local load of this CPU, while the power of other components of the system, e.g., a graphics processor, remains uncontrolled.
Other existing power management techniques may manage total power supplied to the system based on the total load of the system.